Publications


SEARCH for SOURCES of HIGH-ENERGY NEUTRONS with FOUR YEARS of DATA from the ICETOP DETECTOR

Astrophysical Journal 830 (2016)

MG Aartsen, K Abraham, M Ackermann, J Adams, JA Aguilar, M Ahlers, M Ahrens, D Altmann, K Andeen, T Anderson, I Ansseau, G Anton, M Archinger, C Argüelles, J Auffenberg, S Axani, X Bai, SW Barwick, V Baum, R Bay, JJ Beatty, JB Tjus, KH Becker, S Benzvi, P Berghaus, D Berley, E Bernardini, A Bernhard, DZ Besson, G Binder, D Bindig, M Bissok, E Blaufuss, S Blot, C Bohm, M Börner, F Bos, D Bose, S Böser, O Botner, J Braun, L Brayeur, HP Bretz, A Burgman, T Carver, M Casier, E Cheung, D Chirkin, A Christov, K Clark, L Classen, S Coenders, GH Collin, JM Conrad, DF Cowen, R Cross, M Day, JPAMD André, CD Clercq, EDP Rosendo, H Dembinski, SD Ridder, P Desiati, KDD Vries, GD Wasseige, MD With, T Deyoung, JC Díaz-Vélez, VD Lorenzo, H Dujmovic, JP Dumm, M Dunkman, B Eberhardt, T Ehrhardt, B Eichmann, P Eller, S Euler, PA Evenson, S Fahey, AR Fazely, J Feintzeig, J Felde, K Filimonov, C Finley, S Flis, CC Fösig, A Franckowiak, E Friedman, T Fuchs, TK Gaisser, J Gallagher, L Gerhardt, K Ghorbani, W Giang, L Gladstone, M Glagla

© 2016. The American Astronomical Society. All rights reserved..IceTop is an air-shower array located on the Antarctic ice sheet at the geographic South Pole. IceTop can detect an astrophysical flux of neutrons from Galactic sources as an excess of cosmic-ray air showers arriving from the source direction. Neutrons are undeflected by the Galactic magnetic field and can typically travel 10 (E/PeV) pc before decay. Two searches are performed using 4 yr of the IceTop data set to look for a statistically significant excess of events with energies above 10 PeV (1016 eV) arriving within a small solid angle. The all-sky search method covers from -90° to approximately -50° in declination. No significant excess is found. A targeted search is also performed, looking for significant correlation with candidate sources in different target sets. This search uses a higher-energy cut (100 PeV) since most target objects lie beyond 1 kpc. The target sets include pulsars with confirmed TeV energy photon fluxes and high-mass X-ray binaries. No significant correlation is found for any target set. Flux upper limits are determined for both searches, which can constrain Galactic neutron sources and production scenarios.


Spherical shock in the presence of an external magnetic field

Journal of Physics: Conference Series 688 (2016)

Y Kuramitsu, S Matsukiyo, S Isayama, D Harada, T Oyama, R Fujino, Y Sakawa, T Morita, Y Yamaura, T Ishikawa, T Moritaka, T Sano, K Tomita, R Shimoda, Y Sato, K Uchino, A Pelka, R Crowston, N Woolsey, G Gregori, M Koenig, DW Yuan, CL Yin, YT Li, K Zhang, JY Zhong, FL Wang, N Ohnishi, K Nagamine, H Yoneda, H Takabe

© Published under licence by IOP Publishing Ltd.We investigate spherical collisionless shocks in the presence of an external magnetic field. Spherical collisionless shocks are common resultant of interactions between a expanding plasma and a surrounding plasma, such as the solar wind, stellar winds, and supernova remnants. Anisotropies often observed in shock propagations and their emissions, and it is widely believed a magnetic field plays a major role. Since the local observations of magnetic fields in astrophysical plasmas are not accessible, laboratory experiments provide unique capability to investigate such phenomena. We model the spherical shocks in the universe by irradiating a solid spherical target surrounded by a plasma in the presence of a magnetic field. We present preliminary results obtained by shadowgraphy.


Searches for Sterile Neutrinos with the IceCube Detector.

Physical review letters 117 (2016) 071801-

MG Aartsen, K Abraham, M Ackermann, J Adams, JA Aguilar, M Ahlers, M Ahrens, D Altmann, K Andeen, T Anderson, I Ansseau, G Anton, M Archinger, C Argüelles, TC Arlen, J Auffenberg, S Axani, X Bai, SW Barwick, V Baum, R Bay, JJ Beatty, J Becker Tjus, KH Becker, S BenZvi, P Berghaus, D Berley, E Bernardini, A Bernhard, DZ Besson, G Binder, D Bindig, E Blaufuss, S Blot, DJ Boersma, C Bohm, M Börner, F Bos, D Bose, S Böser, O Botner, J Braun, L Brayeur, HP Bretz, A Burgman, J Casey, M Casier, E Cheung, D Chirkin, A Christov, K Clark, L Classen, S Coenders, GH Collin, JM Conrad, DF Cowen, AH Cruz Silva, J Daughhetee, JC Davis, M Day, JP de André, C De Clercq, E Del Pino Rosendo, H Dembinski, S De Ridder, P Desiati, KD de Vries, G de Wasseige, M de With, T DeYoung, JC Díaz-Vélez, V di Lorenzo, H Dujmovic, JP Dumm, M Dunkman, B Eberhardt, T Ehrhardt, B Eichmann, S Euler, PA Evenson, S Fahey, AR Fazely, J Feintzeig, J Felde, K Filimonov, C Finley, S Flis, CC Fösig, T Fuchs, TK Gaisser, R Gaior, J Gallagher, L Gerhardt, K Ghorbani, W Giang, L Gladstone, T Glüsenkamp, A Goldschmidt, G Golup, JG Gonzalez, D Góra, D Grant, Z Griffith, A Haj Ismail, A Hallgren, F Halzen, E Hansen, K Hanson, D Hebecker, D Heereman, K Helbing, R Hellauer, S Hickford, J Hignight, GC Hill, KD Hoffman, R Hoffmann, K Holzapfel, A Homeier, K Hoshina, F Huang, M Huber, W Huelsnitz, K Hultqvist, S In, A Ishihara, E Jacobi, GS Japaridze, M Jeong, K Jero, BJ Jones, M Jurkovic, A Kappes, T Karg, A Karle, U Katz, M Kauer, A Keivani, JL Kelley, A Kheirandish, M Kim, T Kintscher, J Kiryluk, T Kittler, SR Klein, G Kohnen, R Koirala, H Kolanoski, L Köpke, C Kopper, S Kopper, DJ Koskinen, M Kowalski, K Krings, M Kroll, G Krückl, C Krüger, J Kunnen, S Kunwar, N Kurahashi, T Kuwabara, M Labare, JL Lanfranchi, MJ Larson, D Lennarz, M Lesiak-Bzdak, M Leuermann, L Lu, J Lünemann, J Madsen, G Maggi, KB Mahn, S Mancina, M Mandelartz, R Maruyama, K Mase, R Maunu, F McNally, K Meagher, M Medici, M Meier, A Meli, T Menne, G Merino, T Meures, S Miarecki, E Middell, L Mohrmann, T Montaruli, M Moulai, R Nahnhauer, U Naumann, G Neer, H Niederhausen, SC Nowicki, DR Nygren, A Obertacke Pollmann, A Olivas, A Omairat, A O'Murchadha, T Palczewski, H Pandya, DV Pankova, JA Pepper, C Pérez de Los Heros, C Pfendner, D Pieloth, E Pinat, J Posselt, PB Price, GT Przybylski, M Quinnan, C Raab, M Rameez, K Rawlins, M Relich, E Resconi, W Rhode, M Richman, B Riedel, S Robertson, C Rott, T Ruhe, D Ryckbosch, D Rysewyk, L Sabbatini, J Salvado, SE Sanchez Herrera, A Sandrock, J Sandroos, S Sarkar, K Satalecka, P Schlunder, T Schmidt, S Schöneberg, A Schönwald, D Seckel, S Seunarine, D Soldin, M Song, GM Spiczak, C Spiering, M Stamatikos, T Stanev, A Stasik, A Steuer, T Stezelberger, RG Stokstad, A Stößl, R Ström, NL Strotjohann, GW Sullivan, M Sutherland, H Taavola, I Taboada, J Tatar, S Ter-Antonyan, A Terliuk, G Tešić, S Tilav, PA Toale, MN Tobin, S Toscano, D Tosi, M Tselengidou, A Turcati, E Unger, M Usner, S Vallecorsa, J Vandenbroucke, N van Eijndhoven, S Vanheule, M van Rossem, J van Santen, J Veenkamp, M Voge, M Vraeghe, C Walck, A Wallace, N Wandkowsky, C Weaver, C Wendt, S Westerhoff, BJ Whelan, K Wiebe, L Wille, DR Williams, L Wills, H Wissing, M Wolf, TR Wood, E Woolsey, K Woschnagg, DL Xu, XW Xu, Y Xu, JP Yanez, G Yodh, S Yoshida, M Zoll

The IceCube neutrino telescope at the South Pole has measured the atmospheric muon neutrino spectrum as a function of zenith angle and energy in the approximate 320 GeV to 20 TeV range, to search for the oscillation signatures of light sterile neutrinos. No evidence for anomalous ν_{μ} or ν[over ¯]_{μ} disappearance is observed in either of two independently developed analyses, each using one year of atmospheric neutrino data. New exclusion limits are placed on the parameter space of the 3+1 model, in which muon antineutrinos experience a strong Mikheyev-Smirnov-Wolfenstein-resonant oscillation. The exclusion limits extend to sin^{2}2θ_{24}≤0.02 at Δm^{2}∼0.3  eV^{2} at the 90% confidence level. The allowed region from global analysis of appearance experiments, including LSND and MiniBooNE, is excluded at approximately the 99% confidence level for the global best-fit value of |U_{e4}|^{2}.


Turbulent dynamo in a collisionless plasma

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 113 (2016) 3950-3953

F Rincon, F Califano, AA Schekochihin, F Valentini


Laboratory astrophysical collisionless shock experiments on Omega and NIF

Journal of Physics: Conference Series 688 (2016)

HS Park, JS Ross, CM Huntington, F Fiuza, D Ryutov, D Casey, RP Drake, G Fiksel, D Froula, G Gregori, NL Kugland, C Kuranz, MC Levy, CK Li, J Meinecke, T Morita, R Petrasso, C Plechaty, B Remington, Y Sakawa, A Spitkovsky, H Takabe, AB Zylstra

© Published under licence by IOP Publishing Ltd.We are performing scaled astrophysics experiments on Omega and on NIF. Laser driven counter-streaming interpenetrating supersonic plasma flows can be studied to understand astrophysical electromagnetic plasma phenomena in a controlled laboratory setting. In our Omega experiments, the counter-streaming flow plasma state is measured using Thomson scattering diagnostics, demonstrating the plasma flows are indeed super-sonic and in the collisionless regime. We observe a surprising additional electron and ion heating from ion drag force in the double flow experiments that are attributed to the ion drag force and electrostatic instabilities. [1] A proton probe is used to image the electric and magnetic fields. We observe unexpected large, stable and reproducible electromagnetic field structures that arise in the counter-streaming flows [2]. The Biermann battery magnetic field generated near the target plane, advected along the flows, and recompressed near the midplane explains the cause of such self-organizing field structures [3]. A D3He implosion proton probe image showed very clear filamentary structures; three-dimensional Particle-In-Cell simulations and simulated proton radiography images indicate that these filamentary structures are generated by Weibel instabilities and that the magnetization level (ratio of magnetic energy over kinetic energy in the system) is ∼0.01 [4]. These findings have very high astrophysical relevance and significant implications. We expect to observe true collisionless shock formation when we use >100 kJ laser energy on NIF.


Rejuvenation of stellar mergers and the origin of magnetic fields in massive stars

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 457 (2016) 2355-2365

FRN Schneider, P Podsiadlowski, N Langer, N Castro, L Fossati


Marginal evidence for cosmic acceleration from Type Ia supernovae

Scientific Reports Nature Publishing 6 (2016) 35596

JT Nielsen, A Guffanti, S Sarkar

The ‘standard’ model of cosmology is founded on the basis that the expansion rate of the universe is accelerating at present — as was inferred originally from the Hubble diagram of Type Ia supernovae. There exists now a much bigger database of supernovae so we can perform rigorous statistical tests to check whether these ‘standardisable candles’ indeed indicate cosmic acceleration. Taking account of the empirical procedure by which corrections are made to their absolute magnitudes to allow for the varying shape of the light curve and extinction by dust, we find, rather surprisingly, that the data are still quite consistent with a constant rate of expansion.


Frames of most uniform Hubble flow

Journal of Cosmology and Astroparticle Physics 2016 (2016)

D Kraljic, S Sarkar

© 2016 IOP Publishing Ltd and Sissa Medialab srl .It has been observed [1,2] that the locally measured Hubble parameter converges quickest to the background value and the dipole structure of the velocity field is smallest in the reference frame of the Local Group of galaxies. We study the statistical properties of Lorentz boosts with respect to the Cosmic Microwave Background frame which make the Hubble flow look most uniform around a particular observer. We use a very large N-Body simulation to extract the dependence of the boost velocities on the local environment such as underdensities, overdensities, and bulk flows. We find that the observation [1,2] is not unexpected if we are located in an underdensity, which is indeed the case for our position in the universe. The amplitude of the measured boost velocity for our location is consistent with the expectation in the standard cosmology.


The nature and energetics of AGN-driven perturbations in the hot gas in the Perseus Cluster

Monthly Notices of the Royal Astronomical Society 458 (2016) 2902-2915

I Zhuravleva, E Churazov, P Arévalo, AA Schekochihin, WR Forman, SW Allen, A Simionescu, R Sunyaev, A Vikhlinin, N Werner

© 2016 The Authors.Cores of relaxed galaxy clusters are often disturbed by AGN. Their Chandra observations revealed a wealth of structures induced by shocks, subsonic gas motions, bubbles of relativistic plasma, etc. In this paper, we determine the nature and energy content of gas fluctuations in the Perseus core by probing statistical properties of emissivity fluctuations imprinted in the soft and hard-band X-ray images. About 80 per cent of the total variance of perturbations on ~8-70 kpc scales in the core have an isobaric nature, i.e. are consistent with subsonic displacements of the gas in pressure equilibrium with the ambient medium. The observed variance translates to the ratio of energy in perturbations to thermal energy of ~13 per cent. In the region dominated by weak 'ripples', about half of the total variance is associated with isobaric perturbations on scales of a few tens of kpc. If these isobaric perturbations are induced by buoyantly rising bubbles, then these results suggest that most of the AGN-injected energy should first go into bubbles rather than into shocks. Using simulations of a shock propagating through the Perseus atmosphere, we found that models reproducing the observed features of a central shock have more than 50 per cent of the AGN-injected energy associated with the bubble enthalpy and only about 20 per cent is carried away with the shock. Such energy partition is consistent with the AGN-feedback model, mediated by bubbles of relativistic plasma, and supports the importance of turbulence in the cooling-heating balance.


Age-velocity dispersion relations and heating histories in disc galaxies

Monthly Notices of the Royal Astronomical Society 462 (2016) 1697-1713

M Aumer, J Binney, R Schönrich

© 2016 The Authors.We analyse the heating of stellar discs by non-axisymmetric structures and giant molecular clouds (GMCs) in N-body simulations of growing disc galaxies. The analysis resolves long-standing discrepancies between models and data by demonstrating the importance of distinguishing between measured age-velocity dispersion relations (AVRs) and the heating histories of the stars that make up the AVR. We fit both AVRs and heating histories with formulae ∝tβ and determine the exponents βR and βz derived from in-plane and vertical AVRs and β~R and β~z from heating histories. Values of βz are in almost all simulations larger than values of β~z, whereas values of βR are similar to or mildly larger than values of β~R. Moreover, values of βz (β~z) are generally larger than values of βR (β~R). The dominant cause of these relations is the decline over the life of the disc in importance of GMCs as heating agents relative to spiral structure and the bar. We examine how age errors and biases in solar neighbourhood surveys influence the measured AVR: they tend to decrease β values by smearing out ages and thus measured dispersions. We compare AVRs and velocity ellipsoid shapes σz/σR from simulations to solar neighbourhood data. We conclude that for the expected disc mass and dark halo structure, combined GMC and spiral/bar heating can explain the AVR of the Galactic thin disc. Strong departures of the disc mass or the dark halo structure from expectation spoil fits to the data.


Characterizing stellar halo populations - I. An extended distribution function for halo K giants

Monthly Notices of the Royal Astronomical Society 460 (2016) 1725-1738

P Das, J Binney

© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.We fit an extended distribution function (EDF) to K giants in the Sloan Extension for Galactic Understanding and Exploration survey. These stars are detected to radii ~80 kpc and span a wide range in [Fe/H]. Our EDF, which depends on [Fe/H] in addition to actions, encodes the entanglement of metallicity with dynamics within the Galaxy's stellar halo. Our maximum-likelihood fit of the EDF to the data allows us to model the survey's selection function. The density profile of the K giants steepens with radius from a slope ~-2 to ~-4 at large radii. The halo's axis ratio increases with radius from 0.7 to almost unity. The metal-rich stars are more tightly confined in action space than the metal-poor stars and form a more flattened structure. A weak metallicity gradient ~-0.001 dex kpc-1, a small gradient in the dispersion in [Fe/H] of ~0.001 dex kpc-1, and a higher degree of radial anisotropy in metal-richer stars result. Lognormal components with peaks at ~-1.5 and ~-2.3 are required to capture the overall metallicity distribution, suggestive of the existence of two populations of K giants. The spherical anisotropy parameter varies between 0.3 in the inner halo to isotropic in the outer halo. If the Sagittarius stream is included, a very similar model is found but with a stronger degree of radial anisotropy throughout.


Evidence that the maximum electron energy in hotspots of FR II galaxies is not determined by synchrotron cooling

Monthly Notices of the Royal Astronomical Society 460 (2016) 3554-3562

AT Araudo, AR Bell, A Crilly, KM Blundell

© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.It has been suggested that relativistic shocks in extragalactic sources may accelerate the highest energy cosmic rays. The maximum energy to which cosmic rays can be accelerated depends on the structure of magnetic turbulence near the shock but recent theoretical advances indicate that relativistic shocks are probably unable to accelerate particles to energies much larger than a PeV. We study the hotspots of powerful radiogalaxies, where electrons accelerated at the termination shock emit synchrotron radiation. The turnover of the synchrotron spectrum is typically observed between infrared and optical frequencies, indicating that the maximum energy of non-thermal electrons accelerated at the shock is ≲ TeV for a canonical magnetic field of ~100 μG. Based on theoretical considerations we show that this maximum energy cannot be constrained by synchrotron losses as usually assumed, unless the jet density is unreasonably large and most of the jet upstream energy goes to non-thermal particles. We test this result by considering a sample of hotspots observed with high spatial resolution at radio, infrared and optical wavelengths.


Magnetic field generation during intense laser channelling in underdense plasma

Physics of Plasmas 23 (2016)

AG Smyth, G Sarri, M Vranic, Y Amano, D Doria, E Guillaume, H Habara, R Heathcote, G Hicks, Z Najmudin, H Nakamura, PA Norreys, S Kar, LO Silva, KA Tanaka, J Vieira, M Borghesi

© 2016 Author(s).Channel formation during the propagation of a high-energy (120 J) and long duration (30 ps) laser pulse through an underdense deuterium plasma has been spatially and temporally resolved via means of a proton imaging technique, with intrinsic resolutions of a few μm and a few ps, respectively. Conclusive proof is provided that strong azimuthally symmetric magnetic fields with a strength of around 0.5 MG are created inside the channel, consistent with the generation of a collimated beam of relativistic electrons. The inferred electron beam characteristics may have implications for the cone-free fast-ignition scheme of inertial confinement fusion.


Torus mapper: a code for dynamical models of galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 456 (2016) 1982-1998

J Binney, PJ McMillan


A review of action estimation methods for galactic dynamics

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 457 (2016) 2107-2121

JL Sanders, J Binney


The quiescent phase of galactic disc growth

Monthly Notices of the Royal Astronomical Society 459 (2016) 3326-3348

M Aumer, J Binney, R Schönrich

© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.We perform a series of controlled N-body simulations of growing disc galaxies within non-growing, live dark matter haloes of varying mass and concentration. Our initial conditions include either a low-mass disc or a compact bulge. New stellar particles are continuously added on near-circular orbits to the existing disc, so spiral structure is continuously excited. To study the effect of combined spiral and giant molecular cloud (GMC) heating on the discs, we introduce massive, short-lived particles that sample a GMC mass function. An isothermal gas component is introduced for a subset of the models. We perform a resolution study and vary parameters governing the GMC population, the histories of star formation and radial scale growth. Models with GMCs and standard values for the disc mass and halo density provide the right level of self-gravity to explain the age-velocity dispersion relation of the solar neighbourhood (Snhd). GMC heating generates remarkably exponential vertical profiles with scaleheights that are radially constant and agree with observations of galactic thin discs. GMCs are also capable of significantly delaying bar formation. The amount of spiral-induced radial migration agrees with what is required for the metallicity distribution of the Snhd. However, in our standard models, the outward-migrating populations are not hot enough vertically to create thick discs. Thick discs can form in models with high baryon fractions, but the corresponding bars are too long, the young stellar populations too hot and the discs flare considerably.


Sherlock et al. Reply:

Physical Review Letters 116 (2016)

M Sherlock, W Rozmus, EG Hill, SJ Rose


Thomson scattering measurement of a collimated plasma jet generated by a high-power laser system

Journal of Physics: Conference Series 688 (2016)

T Ishikawa, Y Sakawa, T Morita, Y Yamaura, Y Kuramitsu, T Moritaka, T Sano, R Shimoda, K Tomita, K Uchino, S Matsukiyo, A Mizuta, N Ohnishi, R Crowston, N Woolsey, H Doyle, G Gregori, M Koenig, C Michaut, A Pelka, D Yuan, Y Li, K Zhang, J Zhong, F Wang, H Takabe

© Published under licence by IOP Publishing Ltd.One of the important and interesting problems in astrophysics and plasma physics is collimation of plasma jets. The collimation mechanism, which causes a plasma flow to propagate a long distance, has not been understood in detail. We have been investigating a model experiment to simulate astrophysical plasma jets with an external magnetic field [Nishio et al., EPJ. Web of Conferences 59, 15005 (2013)]. The experiment was performed by using Gekko XII HIPER laser system at Institute of Laser Engineering, Osaka University. We shot CH plane targets (3 mm × 3 mm × 10 μm) and observed rear-side plasma flows. A collimated plasma flow or plasma jet was generated by separating focal spots of laser beams. In this report, we measured plasma jet structure without an external magnetic field with shadowgraphy, and simultaneously measured the local parameters of the plasma jet, i.e., electron density, electron and ion temperatures, charge state, and drift velocity, with collective Thomson scattering.


Proton imaging of an electrostatic field structure formed in laser-produced counter-streaming plasmas

Journal of Physics: Conference Series 688 (2016)

T Morita, NL Kugland, W Wan, R Crowston, RP Drake, F Fiuza, G Gregori, C Huntington, T Ishikawa, M Koenig, C Kuranz, MC Levy, D Martinez, J Meinecke, F Miniati, CD Murphy, A Pelka, C Plechaty, R Presura, N Quirós, BA Remington, B Reville, JS Ross, DD Ryutov, Y Sakawa, L Steele, H Takabe, Y Yamaura, N Woolsey, HS Park

© Published under licence by IOP Publishing Ltd.We report the measurements of electrostatic field structures associated with an electrostatic shock formed in laser-produced counter-streaming plasmas with proton imaging. The thickness of the electrostatic structure is estimated from proton images with different proton kinetic energies from 4.7 MeV to 10.7 MeV. The width of the transition region is characterized by electron scale length in the laser-produced plasma, suggesting that the field structure is formed due to a collisionless electrostatic shock.


Radio Galaxy Zoo: Discovery of a poor cluster through a giant wide-angle tail radio galaxy

Monthly Notices of the Royal Astronomical Society 460 (2016) 2376-2384

JK Banfield, H Andernach, AD Kapińska, L Rudnick, MJ Hardcastle, G Cotter, S Vaughan, TW Jones, I Heywood, JD Wing, OI Wong, T Matorny, IA Terentev, R López-Sánchez, RP Norris, N Seymour, SS Shabala, KW Willett

© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.We have discovered a previously unreported poor cluster of galaxies (RGZ-CL J0823.2+0333) through an unusual giant wide-angle tail radio galaxy found in the Radio Galaxy Zoo project. We obtained a spectroscopic redshift of z = 0.0897 for the E0-type host galaxy, 2MASX J08231289+0333016, leading to Mr = -22.6 and a 1.4 GHz radio luminosity density of L1.4 = 5.5 × 1024 W Hz-1. These radio and optical luminosities are typical for wide-angle tailed radio galaxies near the borderline between Fanaroff-Riley classes I and II. The projected largest angular size of ≈8 arcmin corresponds to 800 kpc and the full length of the source along the curved jets/trails is 1.1 Mpc in projection. X-ray data from the XMM-Newton archive yield an upper limit on the X-ray luminosity of the thermal emission surrounding RGZ J082312.9+033301 at 1.2-2.6 × 1043 erg s-1 for assumed intracluster medium temperatures of 1.0-5.0 keV. Our analysis of the environment surrounding RGZ J082312.9+033301 indicates that RGZ J082312.9+033301 lies within a poor cluster. The observed radio morphology suggests that (a) the host galaxy is moving at a significant velocity with respect to an ambient medium like that of at least a poor cluster, and that (b) the source may have had two ignition events of the active galactic nucleus with 107 yr in between. This reinforces the idea that an association between RGZ J082312.9+033301 and the newly discovered poor cluster exists.